University of Newcastle upon Tyne School of Mechanical & Systems Engineering

MEC3096 Research Project

By Jean-Christophe Andre

072537523

SupervisedBy

Dr. Francis James Franklin 23rd April 2010

Design and build of a rail buggy

Abstract

This paper describes the processes taken to design and build a rail buggy with a certain set of criteria. These including good wheel to rail contact, a lightweight structure which allows a single person to carry the trolley, the possibility to go on different rail gauges selected and the possibility to add equipment for measuring and analysing rails. The direction of this project was to come up with a four wheel trolley which goes on rails and allows a range of uses. An ongoing issue with miniature structures used on rails is that they tend to be more susceptible to defects in the rails such as the separation between rail sections.The design process involved many stages in which a fully operational rail boggy was generated. It consists of an aluminium square tube frame which overhangs the rails, this offers an effective working surface to install or carry instruments, and a lightweight body to create a product transportable by a single person. The wheels used are made out of acetal as the properties of the material were satisfactory for this purpose, they also offered a much lighter solution to its counterpart made of steel. The wheel was 121mm diameter at the highest point and was mounted on a 25mm diameter shaft. To harbour such a shaft, pedestal bearing units were used allowing an easy connection method for an overhanging structure. In the attempt to reduce the vibrations transmitted from the wheels to the frame, rocksilk insulating material was used between a steel plate connected to the bearings and an aluminium plate connected to the square tubes in the body of the trolley.The university manufactured most of the rail boggy with the exception of the wheels which had to be outsourced due to their complex train wheel profile. The other component produced by an exterior company was the steel plate which required accurate tolerances in its cutting process. The assembly of the trolley did encounter some issues but none which affected the completion of the rail buggy. The final product was then tested at an operational train yard where it was observed that the design of the trolley had achieved its aims and could successfully run up and down the rail without any problems. A few existing railway obstructions had been overlooked in the design process, such as third rails and rail crossings. The first one of these obstructions did not affect the trolley due its small width but the rail crossings did come as a major issue due to the bearing housings being lower than the surface of the wheel in contact with the rails.As such, achieving all the aims set out at the beginning of the project, the rail boggy could be described as a success. This said, the final design would require a few minor adjustments to be fully operational and potentially marketable.

Contents

1.Introduction 1

2.Research 2-4

3.Design Process 4-21

3.1 Structure 4-11

3.2 Wheels 12-14

3.3 Gauge Lengths 14-16

3.4 Potential for Additions 16-17

3.5 Mass of Trolley 17-19

3.6 Cost 19-21

4.Building and Testing 22-27

4.1 Building 22-23

4.2 Testing at Barrow Hill Train Yard 23-27

5.Design Review 27-28

6.Conclusion 29

7.References 30

8.Appendix 31-40

1.Introduction

This paper illustrates the design process and constraints in the build of a track buggy. A light weight, four wheel trolley with suitable structure allowing the incorporation of rail monitoring equipment. This project is not focused on measuring instrumentation used in railway studies; as such only a brief discussion of this subject will be incorporated in the building and testing part of the paper. The focus will be on good structural integrity and wheel to rail contact of the rail buggy. Trains have been around for more than a century and aspects in maintenance, efficiency, reliability, wheel contact and structural behaviour are widely researched as this mean of transportation is continually improved and rendered safer. The Department for Transport has a set of rail research priorities outlying topics of interest and plans to improve future transport. These can be reduced to two main areas of concern, in which this project was designed in relation to, the improvement in cost and capacity which both require good track design and maintenance to quickly and efficiently identify faults in the system. There are systems in place presently which have as purpose to detect faults such as rapid laser profiling of rails. This rail boggy is for the purpose of more precise monitoring of rails to help in the research and development of the railway industry.

The aims of this project are:

Design and build a light-weight trolley which can be carried, assembled and disassembled by one person

Generate a low cost product which could potentially be marketable Have a track buggy able to go on different rail gauge railways around the world Have a good wheel to rail contact when operated Have the possibility for additions such as a drive system, a laptop and any rail

inspection instrumentation

Instrumentation such as strain gauges and laser profilers were looked at in the design process to help with the direction of the project. The understanding and operation of such instruments was not the direction of this paper and therefore there is not much elaboration on the subject.The main problems faced by a track buggy are caused by the miniature size of the product compared to operating trains. This may cause the trolley to experience a different rolling contact and be much more susceptible to faults and structural aspects of the rails, such as gaps between rail sections which can be from none to 5mm, depending on the purpose of the railway or temperature of the rails. Such an issue was spotted with rescue rail which invoiced a particular difficulty crossing rail sections in some cases due to the small diameter nylon wheels used on the product.

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2.Research

Figure 1. (Transportation rail trolleys ¿¿1,2

There are many different trolleys available on the market which serve a number of diverse applications, some more compact than others. A few examples of trolleys used in the transportation of goods and personnel are shown in figure 1 above. On the left hand side is a rail buggy used for rapid deployment, and is designed for easy and quick assembly. The unit is multi-functional and can be adapted for the transport of equipment or injured passengers to or away from an emergency situation. It has an electric motor providing motion to the operating crew and can be dismantled as seen in the middle diagram. The trolley on the right hand side serves a similar purpose, ‘was designed to provide a small, compact folding unit, with a 250kg carrying capacity that can be disassembled and carried in the boot of a car. The trolley is made up of four components, 2 tray halves and 2 wheel sets. When stored the unit is self contained and easily moved around. The trolley has a failsafe braking system, which means that if the operator lets go or trips, the level is released and the brakes applied. Additionally the wheel sets can be removed from the main carrying tray and the main section carried like a stretcher ’1.Rail trolleys are also used in the maintenance and construction of railways. As renewal projects for the system are common, surveying companies require equipment allowing the monitoring of rails which allow efficient measurements to be taken. This requires equipment adapted to be carried on rails and which can give data required to accomplish the successful completion of these projects. In figure 2 on the following page are two examples of such trolleys, both of which successfully retrieve required data on railways. On the left hand side is a rail boggy which allows ‘independent bi-directional reversible measurement, displays of distance travelled on each rail and calculated centre line, also equipped with centred visible Laser Beam Indicator directed at the track bed or the tunnel wall for accurate verification of guide way elements positioning. The unit is light weight, having a mass of 35 kg, is easily assembled and disassembled allowing it to fit inside a

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compact car ’3. On the right is the Swiss trolley, ‘a multisensory measurement system incorporating real-time kinematic GPS for the surveying of tracks. The University of Applied Sciences of Burgdorf developed the trolley in collaboration with terra international surveys, Switzerland, as part of a project financed by the Commission for Technology and Innovation by the Swiss Office for Professional Education and Technology. It incorporates two tiltmeters, a track gauge measuring system, and odometers enabling the assessment of key parameters: cant, gradient, track gauge, and chaining as well as GPS ¿ RTK ’4.

Figure 2. (Surveying railtrolleys¿¿3,4.

Figure 3. (Analysis rail trolleys¿¿5,6

The other type of rail trolleys used in the industry are for analysis purposes, to implement rail research or in the monitoring of defects. They are used in the development and improvement of railway systems which lead in the progress of maintenance, safety, design and cost. Figure 3 shows two such examples of trolleys used for analysis. On the left hand side, ‘the Corrugation Analysis Trolley is an extremely accurate instrument that can be used to measure rails for acoustics purposes and for Quality Assurance of rail grinding. It has the great attraction that it can be both used and carried by a single person. The equipment, when packed in its flight case, weighs less than 15kg. There are few, if any, instruments that can measure metres of rail with similar accuracy ’5. The unit only allows the analysis of one rail at a time and requires the operator to push it forward as required. On the right hand side is a similar apparatus, used to measure corrugation in rails using eddy current transducers which are very accurate sensors. It is a small portable unit which uses a PDA

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1 Steel frame2 Bearing housing3 M8 steel bolts

interface system to store information, allowing easy transfer and analysis of data. This unit also requires the operator to manual displace the trolley as required.

3.Design Process

3.1 Structure

The structure is the starting point of the design and must respect a set of guidelines such as strength, width, height, length and mass. The first frame offered a flat surface perpendicular and adjacent to the inside of the rail, which was made out of steel as can be seen in Figure 4. A 10mm thick sheet of metal with holes equally spaced on its face to allow anything from instruments to shelves to be added to the structure. The bearing housings were simply connected to the frame through four M8 bolts as seen on the right hand side of Figure 4.

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3

1

Figure 4. (Initial structure)

This frame was analysed using Ansys Workbench to demonstrate the structural properties of the components, more precisely the effect of uniform loading on the frame being held up by four bolts at each end. This model is seen on the following page in Figure 5. The structure is uniformly loaded on the top surface with a load of 52710 N and supported where the bolts should be for the connection to the bearing housings. This load created a peak equivalent Von Mise’s stress of 250 MPa, considering that the ‘average yield stress of medium carbon steel is 602.5 MPa’7 as seen in Table 1 on the following page, this would mean that the structure could support, before plastic deformation, a uniformly distributed 13 tonnes or 127 kN. This component was very heavy and badly suited for allowing the extendibility and retract-ability of the structure to accommodate different rail gauge

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lengths. The design combined with the initial wheel design generated a very complex product, which made entirely out of steel, had a mass of 135kg, which is not a reasonable mass to be carried by a single person. It happened to be over-specified in strength as well for the requirements of the trolley. For these reasons aluminium was selected to replace steel for the frame, a comparison table of the two metals is shown below in Table 1.

Figure 5. (Ansys model of initial frame)

Material Density (kg/m3)

Yield Strength (MPa)

Tensile strength (MPa)

Young’s Modulus (GPa)

Price (£/kg)

Medium Carbon Steel

7800-7900 305-900 410-1200 200-216 0.472-0.519

Aluminium 6082

2670-2730 240-290 280-340 70-74 1.09-1.2

Average Difference

5150(291%)

337.5(227%)

495(260%)

136(289%)

0.6495(43%)

Table 1. (Comparison of Steel to Aluminium ¿¿7

As can be seen in the table above, steel has better properties than aluminium in every aspect shown apart from the density, where aluminium is almost three times lighter. For this reason an appropriate structure had to be designed to replace the original one by a more reasonable structure, which could still support a high load but weighed much less, all

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this by maintaining good structural integrity. To accomplish these goals, square tubes made out of 6082 series aluminium alloy were selected as they offered an easy method for the extendibility of the structure, reasonable strength and presented flat surfaces on every side. The second design of the frame used an “H” style of arrangement of the box sections as seen in Figure 6. This involved two wheel sections which were connected by two middle sections as demonstrated below. The dimensions of the wheel sections were determined by the selection of an ice hockey bag to carry the trolley, which had dimensions ‘914mm x 406mm x 406mm’8. These dimensions represent the maximum area of the bag, therefore considering that each wheel section would have to inserted in this one, a margin of manoeuvre was arbitrarily chosen allowing room for the trolley to fit through the opening of the bag. The dimensions of the frame were therefore selected to be 850mm x 380mm, which gave plenty difference between the size of the bag and that of the wheel sections.

Figure 6. (Second Structure)

Using this style of structure gave the rail buggy a good working surface above the rails, as both 850mm square tubes would be approximately equidistant from the rail, allowing the easy installation of monitoring equipment on the surface of the box sections. The bearings used in this design are “Pedestal bearing units, SKF SY 25 TF”, manufactured by SKF for a 25mm diameter shaft, therefore the shaft being a “LJM linear bearing shaft, steel (SKF), Length: 250mm, Diameter: 25mm”. An Ansys Workbench model was generated to analyses the structural properties of the wheel unit as seen on the following page in figure 7 and 8. A load of 13701 N was applied to each bearing housing with the shaft being constrained in such a way to model the contact effect of the wheel to create accurate readings, this generated a peak equivalent Von Mise’s stress of 250 MPa in the bearings due to the small area of contact of the bearing rollers to the casing. It is reasonable to suggest that the unit could take twice that load before failure knowing that the bearings are made out of high carbon steel and having a yield stress close to ‘500 MPa’7. Operating a bearing near it point of plastic deformation is recommended and therefore a safety factor of 3 would be a reasonable maximum load to be carried by these components as loads may not always be

850mm square tubes

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equally distributed on each bearing unit causing different loading aspects and results. This would mean that each bearing unit could be loaded uniformly with a load of 931kg. This said, by looking at the models below, the shaft does not seem to represent high stress peaks and therefore by itself could potentially carry a much higher load if the bearing were taken out of the equation. The effects on the wheels from such a load were not looked into in this section.

Load Load

Figure 7. (Ansys simulation of load applied on the Wheel Unit)

Figure 8. (Ansys simulation of load applied on the Wheel Unit)

It was seen fit to add a steel and aluminium plates to the wheel unit as shown above, this was carried out to strengthen and stabilise the bearings housings and the whole unit for that matter, which would have a beneficial impact in maintaining the correct alignment of

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the bearings on the shaft, this arrangement can be seen in Figure 9. The use of the aluminium plate was brought forward when rocksilk insulating material was proposed as a damper for the structure; this insulating layer would be gently sandwiched between the two plates and would hopefully dampen any vibrations in the system caused by irregularities in the rails. This arrangement can be seen in figure 9 as well. Steel nuts would firmly fasten the steel plate to the bearing housings for the discussed added strength and stability, this method would also allow the aluminium plate to be gently fastened on top of the rocksilk sheet, allowing the highest damping prospect for the structure as the plate would be resting on the insulation, this restricting as possible the connection with the rest of the wheel unit, (the nuts connecting the steel plate to the bearing housings are not shown in Figure 9). The “rocksilk universal slab” used in this design is 30mm thick and is ‘used for a wide range of thermal and acoustic insulation applications ' 9, the only physical data given on the subject relates to thermal insulating properties of the material. Due to these new design features, a finite element model was generated to assess the physical properties of the new frame and wheel unit, as seen in figure 10 on the following page.

1 5 6

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2

3 7 4

Figure 9. (Final wheel unit design)

1 Aluminium plate (202x250mm) 5 Nylon bush M102 Steel plate 6 M10 hexagon bolts3 Steel bearing shaft 250mm 7 Wheel spacer4 SKF bearing unit 8 Rocksilk insulation

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Figure 10. (Ansys simulation of load uniformly applied to the wheel section)

The model above represents each, “25.4mmx25.4mmx3.25mm”, square tube being uniformly loaded with 18601 N along the whole length, this generating a peak equivalent Von Mises stress of 280 MPa, which is slightly higher than the average yield stress of 6082 grade aluminium and represents the lowest value for the tensile strength of the material. This would mean that the frame would start to plastically deform at an average load of 17605 N (which is a peak stress of ‘265 MPa’7), this represents a uniformly distributed mass of 1795 kg per square tube. This modelling neglects a few issues such as the square tubes being welded to the plate, the plate being fastened in position by bolts and nylon bushes and that the plate is resting on insulation material. Implementing a safety factor of 4 , which considers the factors just presented, allows the wheel section to support up to 449 kg per box section.The steel plate would be in direct contact with the bearing housings, these would be fastened using steel “M10 hexagon head bolts”, which creates an issue with the aluminium plate, as steel in contact with aluminium in a potentially damp environment would generate rapid corrosion, therefore nylon bushes would be used to shield any contact between the two components and materials.The middle box sections would easily be inserted in the wheel sections due to the use of square tubes of different size. Unfortunately box sections which fitted perfectly one into each other could not be found in bulk quantity and therefore sizes chosen created a gap of 3.1mm on each face of the inserting sections. This occurs due to the use of a square tube of 25.4mm and another of 38.1mm both having a 3.25mm thick surface as seen on the following page in figure 11. This issue required a good fastening method which involved two bolts being used to fasten each side of the middle box sections to the 150mm square tube poking out of the wheel section. The bolts were designed to be fitted on different sides of

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the box section, as can be seen in figure 11 by the holes and the dotted lines, obviously the bolts were carefully placed so that they did come into contact. This method resolved the issue of movement in all three axis of the two box sections. Nylon bushes were also used on the 1350mm square tube to make the fastening more precise and to even further reduce the risk of movement (wobbling) in the components whilst being mounted together. To fasten these two components, “Aluminium Alloy Allen Bolts M8x1.25mmx60mm”, were used to prevent any steel to aluminium contact in the structure. Using aluminium bolts does have a number of downfalls, in such that they are much easier to grind, get damaged easily and have a much lower yield strength than their counterpart in steel, which in the case of a load carrying bolt may not be a wise selection but in this particular case were the middle section will not have to support any loads, this selection is acceptable.

Figure 11. (Intersection of square tubes)

This connection was analysed nevertheless, to assess the loading behaviour, tabulate peak stresses, and measure the maximum load allowable in the middle section before plastic deformation occurred. The results of this computer analysis, carried out with “Ansys Workbench”, are shown on the following page in figures 12 and 13.

150mm long square tube connected to the wheel section

1350mm long square tube, middle section

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Figure 12. (Ansys simulation of loading in the middle section of the rail boggy)

Figure 13. (Ansys simulation of loading in the middle section of the rail boggy)

Each of the middle section square tubes were loaded with a uniformly distributed 1217 N when the rail buggy was in its longest gauge length position. It was found that not more than 117kg evenly distributed on each middle section could be supported by the components, more loading would prompt plastic deformation in these members. This maximum load is not a worrying figure as these members support no load in their normal application and were not designed for load carrying purposes, compared to the 850mm long box sections used on the wheel section. The model does neglect contact geometry, in this case the welding of the 150mm box section to the 850mm one which may create different results in a real life application. The complete set of drawings for each components of the rail buggy can be found in the appendix.

Middle section square tube

150mm square tube

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3.2 Wheels

The selection of the wheels was an important step in the design of the trolley, as it would determine the type of rolling contact this one would have with the rails. A number of different types of wheels are used on existing products all giving a unique interaction with the rails for desired purpose. The use of flat, flanged, double flanged or multiple rollers is not the only variety found in wheels, the materials used also differ in most cases. This goes from thermoplastics to metals with a compromise to make between mass and strength.The rail buggy is designed to have a multi-purpose function, and for this reason a train wheel profile was selected to give the trolley a similar rolling contact as this one with the rails but also this would assure the positioning of the trolley and prevent it from going off rails, which is an important aspect due to the possibility of having a motor to power the product. The wheel would be a miniature replica as the manual transportation of an actual train wheel would be unimaginable. The first design was 200mm diameter at the flange’s highest point and 120mm wide. A ‘P8 wheel profile ’10 was selected due to its common use in the United Kingdom, see appendix page 31.The first wheel was designed with inspiration from a formula car, (seen on left hand side of Figure 14 below), inspired by the method in which it was fastened to the structure, using a lip in the interior diameter with added screw holes. To replicate an original train wheel contact, steel was chosen as the material, (seen on right hand side of Figure 14 below for the drawings of this design).

Figure 14. (Primary wheel design)

The design had many draw backs, such as the requirement of unnecessary components to fasten it to the main structure. The mass of the wheel was also significantly high, (11.24kg per wheel) which by themselves made the trolleys weight 44.96kg, this was unreasonable considering that one of aims of the project was to build a rail boggy transportable by a

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single person. The cost per wheel also was significantly high (£260), making this design inadequate to fulfil the aims of the project. A new design was generated to try and rectify some of the negatives of the previous design. This was accomplished by miniaturising the previous wheel whilst keeping the same profile seen in the appendix in page 31. The new direction involved connecting the shaft directly to the wheel by means of interference fit. Using a 25mm diameter shaft required a hole of the same dimension in the centreline of the wheel, and consequently allowed the possibility to reduce the diameter of the wheel to 121mm on the extremity of the flange. Primarily steel was kept as the material of choice for the design, seen in figure 15 on the left hand side, as the first model, which inevitably generated a wheel of significantly high mass, (4.22kg), even with its resizing.

Figure 15. (Final wheel design)

Figure 16. (Drawing of the rail boggy wheel with P8 profile)

This would bring the total mass of the four wheels to 16.87kg which is a great improvement on the first idea but still high. For this reason another alternative was brought forward, a material of which the properties are compared to steel in table 2, bringing down the mass of each wheel to 0.76kg. This material was acetal which comes to the same cost per wheel as the second steel design (£95), making it a great substitution for the wheels. The final design

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for the wheel is shown in figure 16 on the previous page and represented in figure 15 on the right hand side.

Material Density (kg/m3) Yield Strength (MPa)

Tensile Strength (MPa)

Young’s Modulus (GPa)

Medium carbon steel

7800-7900 305-900 410-1200 200-216

Acetal 1390-1430 48.6-72.4 60-89.6 2.5-5Average difference

6440 542 730.2 204.25

Table 2. (Comparison table of acetal and medium carbon steel¿¿7

There is a very large difference between the two materials, but this is a well know fact, polymers are no where near as strong as commonly used metals. This said, in the case of the wheel, a large amount of acetal is used and through some computer modelling it was determined that there would be no issue with taking load, as the acetal wheel would fail at a load of 678kg on each bearing housing compared to the steel design which would fail at a load of 1.4tonnes on each bearing housing. Considering that the bearings would not operate past a load of 931kg per unit, acetal seemed an appropriate selection for the wheels, these models can be observed in the appendix on page 32 and 33.

3.3 Gauge lengths

This section coincides with the structure segment of the paper, as the number of different gauges chosen had to respect the limitations of the structure. A selection of relevant rail gauge lengths had to be selected out of a vast list of global gauge lengths as seen below in figure 17.

Figure 17. (Railway gauge lengths around the world ¿¿11

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The limitations of the structure allowed the extendibility of the trolley at a maximum of 300mm due to having two extensions (square tubes), on the wheel sections of 150mm each. This was an unachievable gauge difference as bolts were required to maintain in position the middle bars to the wheel sections. Relevant rail gauges were chosen arbitrarily to accommodate countries at close proximity to the United Kingdom and commonly used around the world. The gauge lengths selected are shown below in table 3 and have an accumulated total length difference of 233mm which would allow enough room for bolts to be introduced in the system.

Country (ies) Gauge length in mm Difference between lengthsEurope*, North America, China, Northern Africa, Australia, etc.

1435 0mm

Ex-USSR Countries 1520 85mmIreland 1600 165mmSpain 1668 233mmMaximum: 1668 233mm

Table 3. (Chosen rail gauge lengths¿¿11

In this extension system it was noticed that if two bolts were used to fasten one side of the middle square box (1350mm square tube) to the wheel section, were side by side on the same face of the tube there would not be enough room to allow the chose rail gauges to be implemented on the trolley. This arrangement is shown below in figure 18 on the left hand side, instead it was chosen to apply the bolts on the different sides of the square tube, (seen on the right hand side of figure 18), allowing closer proximity of the bolts and therefore all gauge lengths selected in table 3 could be implemented on the rail buggy.

Figure 18. (Fastening of middle section to wheel section)

To calculate the position of the holes in the square tubes connected to the wheel sections (the 150mm square tubes), an appropriate position had to be selected on the wheel for the desired area of contact with the rail. As the gauge length of a railway system is the length of the inside of one rail to the other, it required the selection of the closest section of the

Bolts side by side Bolts opposite sides

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wheel to the flange to be in contact with the rails. This was determined by analysing the wheel profile and selecting an appropriate area of contact which would give the best rolling motion. Shown in figure 19 is the location chosen on the wheel, demarked by the blue line which will coincide with the dimensions representing the gauge length.

Figure 19. (Rail Gauge parameters¿¿11

With this location determined, the positioning of the holes could be carried out on the 150mm square tubes, as shown below on the left hand side in figure 20. The length of the middle section and holes requires could also be determined satisfying the selected gauge lengths, (table 3), as seen below on the right hand side in figure 20.

Figure 20. (Gauge lengths requirements)

3.4 Potential for additions

The rail buggy was designed in function to accommodate a certain amount of commodities such as rail inspection technologies. The layout of the structure gives a great surface to fasten or carry any type of measuring equipment. The trolley was also designed to potentially carry a laptop around whilst undergoing some testing. It was found that the average portable computer had dimensions of 270mm x 210mm to 350mm to 250mm and

Same coordinate

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had a mass between 1kg and 2.5kg, (figures shown are an average of a sample of every day portable computers). The addition of a platform to house a laptop on the unit only requires minor modifications as the frame of the structure allows a great surface for the positioning of this addition. The final additional aspect looked at during the design process was the implementation of a drive system. A battery operated motor which would give automatic motion to the trolley allowing the effortless monitoring of rails. In the first idea for the rail buggy, a shaft connected the rear wheels together facilitating the addition of a driving unit but this design utilised unnecessary material which made the overall mass of the trolley increase. The final design however does not have much extra shaft room to directly connect to a motor and for this reason another solution was brought forward. The use of keyed coupling as seen bellow in figure 21, or welding would be used to transmit the power through the driving shaft.

Figure 21. (‘Keys on shaft section ' ¿¿12

‘In such cases, the key, which is the male portion of the coupling, is on the section of one shaft, and the keyway, which is the female portion of the coupling, is on the section of the other shaft. It is evident that the manufacture of the “key” and the “keyway” has to be precise, so that the former fits snugly into the latter. Precise analysis of keyed analysis couplings is difficult, but an approximate design can be made by assuming that the shear stress distribution in a key varies linearly with the radial distance of a point on the key from the centre of the shaft. When such an approximation design is made, it should be ensured that the “factor of safety” is so large that the “factor of ignorance” is well contained ’ .12

3.5 Mass of trolley

The mass of the trolley was an important criterion in the design process, as the aim of the project was to build a rail buggy which could be transported by a single person. The definition of the maximum mass possible to be carried by a person differs in all situations, therefore the objective became to design the lightest trolley possible, which could still

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accomplish its desired requirements. The weight limitation of the carrying bags was also a physical limitation for the rail buggy, mentioned latter on in this section.As the project evolved, great improvements were done in relation to this subject by the selection of better materials and modifications in the design. In Table 4 below, is the comparison of the different structures designed through this project, as can be seen, there is a vast improvement from the first trolley to the second, this was largely due to a change of material in the framework, going from steel (density of 7800-7900kg/m3), to aluminium (density of 2670-2730kg/m3). There was also a large change in the shape of the design which further reduced the mass of the rail buggy. The mass did increased from the second design to the final one, due to a few modifications to strengthen the previous idea and increase the structural integrity of the trolley as previously discussed in the structure section of the design process.

Design

Original design Second design Final designMain structural change

- Used of aluminium square tubes

Implementation of a steel & aluminium plates

Mass 89.81kg 18.14kg 23.53kgMass difference with previous design

0kg -71.67kg +5.39kg

Mass difference with original design

0kg -71.67kg -66.28kg

Table 4. (Mass of the structures)

Design

First wheel design Second wheel design Final wheel designMaterial Steel Steel AcetalMass per wheel 11.24kg 4.22kg 0.763kgCumulative (x4) 44.96kg 16.88kg 3.052kgMass loss per wheel on original design

0kg 7.02kg 10.48kg

Mass loss overall on original design

0kg 28.08kg 41.91kg

Table 5. (Mass of the wheels)

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As can be seen in the mass of the wheels table on the previous page, the modifications done throughout the design process had a very large impact on the mass of the trolley. This achieved a final design (23.53kg), which was almost two times lighter than the wheels on the initial design (44.96kg). The breakdown of the mass of each component in the final design is shown below in table 6. As mentioned previously, the bag carrying the trolley was a limitation to the final weight of the product, as such, an ice hockey bag would be used to carry the rail buggy around as it can easily take up to 30 kilograms of load without failing. The bag was chosen in function that it allowed the possibility to carry extra tools and instrumentation as desired without any problems of overloading causing the failure of this one.

Component Mass of component (kg) Qty Total mass subjected to the trolley (kg)

150mm Al square tube 0.11 4 0.44 850mm Al square tube 0.66 4 2.66 1350mm Al square tube 1.65 2 3.3 Aluminium plate 0.41 4 1.62 Steel plate 0.61 4 2.43 Rocksilk insulating block 0.15 4 0.61 250mm steel bearing shaft

0.96 4 3.85

SKF bearing 0.90 8 7.16 All bolts, bolt heads, washers and nylon bushes

0.08 NA 1.46

TOTAL MASS: 23.53Table 6. (Breakdown of rail boggy mass)

3.6 Cost

The management of cost in a project is vital as it is the difference between a product which is marketable and a product which is unaffordable. The main issue with building a light weight trolley, is a problem well known in the car industry for instance, as light materials with great physical properties, (yield strength, tensile strength and Young’s modulus) are generally considerably more expensive as raw materials. This issue is vastly noticed in this project, considering the variations between aluminium and steel or even steel and acetal, which in this case engendered a visible increase in the cost of the rail buggy. The matter surrounding manufacturing cost was not of great concern in this particular project as the labour did not add to the final cost of the project, mainly undertook by university technicians which cooperated in the work required for the trolley.A commonly used bolt, nut and washer which does not oxidise even with the contact with other more reactive metals is stainless steel, compared to aluminium this metal is much

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stronger, as demonstrated in Table 7 below, being very similar to medium carbon steel in its physical properties. This would have been a viable option instead of using aluminium components which were not recommended in wear and high loading situations. Nevertheless in this situation the bolts in question, (“M8 allen bolts, aluminium alloy”), fastened a member with would support no load and therefore the cheapest options was preferred. Table 8 below compares the exact same component in aluminium to stainless steel to demonstrate the existing differences.Material Cost (£/kg) Yield Stress (MPa)Stainless 4.58-5.04 585Aluminium Alloy 6000 series 1.09-1.2 265From Bottom to Top Difference (%)

420 221

Table 7. (Comparison between stainless steel and 6000 series aluminium alloy ¿¿7

Component 1 Cost per unit (£) Stainless Steel

% increase in cost from right to left

Cost per unit (£) Aluminium alloy

M 8 Allen bolts 60mm

2.43 221 1.10

M 8 hexagon full nuts

0.15 25 0.59

M 8 flat washers

0.09 18 0.51

Table 8. (Comparison between stainless steel and aluminium components ¿¿13

Stainless steel is on average 4 times more expensive than its counterpart aluminium but this does not reflect the values observed for the components. One reason for this, is the greater popularity of the stainless steel components as aluminium alloy bolts, nuts and washers are practically specialist components. This said the quantities available for the stainless steel components would have increased the cost of the project, as a bag of 25, “M 8 Allen bolts 60mm”, stainless steel, comes at £60.85, which is £33.71 more expensive than all the aluminium bolts, nuts and washers.The outsourcing of the manufacture was only required in two instances, for the P8 profile acetal wheels, as the university did not have the required tooling and expertise to generate this component and also for the steel plate which required good quality laser cutting. This did have an impact on the cost of these particular components due to the cost of labour being introduced in the component and tooling, which is a more realistic representation of manufacturing costs in the real world. A breakdown of the cost of each component used in the rail boggy is shown in table 9 below.

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Components Supplier Price exc. VAT

Qty

Total cost exc. VAT (£)

Acetal wheel with P8 profile Bill Quay 93.00 4 372.00M10 hexagon head set screws, 60mm minimum length

SIG Fixings/Max Wilson - 20 7.41

M10 hexagon full nuts SIG Fixings/MaxWilson - 40 2.86M10 flat washers SIG Fixings/Max Wilson - 60 1.62LJM linear bearing shaft, steel (SKF), Length: 1m, Diameter: 25mm

RS Components 35.97 1 35.97

Pedestal bearing unit, SKF SY 25 TF RS Components 20.30 8 162.40Aluminium 6082 box section: 1”x1”x10gx5.0m

Holmes Dodsworth Metals Ltd 32.00 1 32.00

Aluminium 6082 box section: 1.5”x1.5”x10gx6.0m

Holme Dodsworth Metals Ltd 64.00 1 64.00

Aluminium 6082 sheet: 250x250x3mm Holme Dodsworth Metals Ltd 6.20 4 24.8233x202x3mm w/holes & ap, 3mm Mild Steel 43A

Acorn Laser Ltd 9.24 4 36.96

Rocksilk Universal Slab RS100 30mmx600x1200 (x10) 7.2m2

Tyne insulation Supplie(r)s Ltd 19.71 1 19.71

Alloy Allen Bolts M8x1.25mmx60mm Blue 5 pack

Pro-Bolt Limited 5.52 2 11.04

Alloy Full Nuts M8 Red 5 pack Pro-Bolt Limited 2.97 2 5.94Alloy Washers M8 Gold 5 pack Pro-Bolt Limited 2.54 4 10.16Nylon Bushes (NB51) Component Force 1.00 16 16.00Nylon Bushes (NB57) Component Force 1.00 24 24.00B/S Bungee Cord 48in 2Pc 45447 Amazon.co.uk 2.02 1 2.026.0mm Hexagon C/V L-Wrench Ball Driver Cromwell Tools Ltd 1.73 2 3.4613mm x 17mm CH/Vanadium O/End Spanner

Cromwell Tools Ltd 4.00 4 16.00

PVC Black Grommet 38.1mm bag 100 RS Components 4.60 1 4.60TPS response ice hockey bag Breakout 35 2 70Total 922.95

Table 9. (Breakdown of cost in the rail boggy)

In most cases, components had to be ordered respecting minimum purchase quantities from the suppliers which inevitably meant that a considerable amount of material would be wasted. This is most noticeable in the purchase of the aluminium square tubes, 6 metres of the “1.5” box section” was ordered but only 2.7 metres were required generating a waste of 3.3 metres of material. The same is present in the “1” box section”, the “M10 hexagon steel bolts”, nuts, washers and “Rocksilk universal slab”. This is a reality in the build of products which engenders an unnecessary higher cost to the project as can be observed in table 9 above.

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4.Building and Testing

4.1 Building

The building process of the rail buggy firstly involved the manufacture of designated components which was carried out for the majority by university technicians through the guidance of engineering drawings which are given in the appendix, meaning all the components of the structure. Components outsourced included the steel plate which was laser cut by “Acorn Laser Ltd” and the wheels which were manufactured by “Bill Quay Engineering”. The insulation material was cut by hand in the workshop personally. The later part of the building involved the assembly of all completed components, which required the design and drawings to have been precise and well thought, to remove any issues in this process. The components made by the university work shop did not require complex tooling as for the great majority they involved drilling and cutting. The most complex job carried out was in the fixing of the wheel section, as it required welding to fasten the 850mm long square tubes to the aluminium plate and the fastening of the 150mm square tubes to the selected 850mm sections, as seen below in figure 22 on the left hand side.

Figure 22. (Structure fittings)

The assembly of the trolley incurred some issues when the shafts were inserted in the wheels. The interference fitting required was not correct on all wheels; in fact only two had the appropriate hole size and interference the wheels, this required a solution to be found to rectify the problem in the other two. The idea of using “Araldite Bonding Adhesive” to solve this problem was presented as a permanent fix but it was found that the spacers used (“black PVC Grommets”), to prevent the wheels from potentially sliding side to side on the shaft acted as retainers and prevented the wheel from freely rotating and sliding on the

Same component

Welded

Welded

Welded

850mm boxsection

150mm boxsection

Aluminium plate

Gap between middle section tubes and 850mm box section

22

shaft. This issue resolved, and the assembly being resumed, another matter came to attention. In the design, a small gap of 1mm, between the middle section square tubes and the 850mm box sections was left for the presence of welding material at that junction for when the shortest rail gauge was the setting on the trolley, (as seen in figure 22 on the right hand side on the previous page). It was noticed during the assembly that not enough big a gap had been left and minor rectification on the middle section were required to allow a good fit, such as chamfering of the interior of the tube and the removal of 1mm to each end face.It was chosen to use two ice hockey bags to transport the rail buggy, allowing a unique bag for each wheel section, reducing the weight per bag to facilitate the job of transportation. This decision did increase the cost of the final project by £70 making the final cost of the project £922.95. The bags were fitted with sheets of insulating material that were left from the project, as can be seen below in figure 23, and wrapped in cling film to water proof the sheets and give a protective layer to the skin irritating insulation. This was done to protect the rail buggy from damaging impact with the ground and to maintain the shape of the bag at all times.

Figure 23. (Insulation plate in the “TPS” ice hockey bags)

4.2 Trolley testing at Barrow Hill train yard

Barrow hill was the setting for the testing and use of the completed rail buggy, as it offered plenty of railway space for the undisturbed observation of the trolleys operations. This allowed the thorough inspection of the trolleys features to determine if the design respected the aims of the project. The first observation carried out was to determine if the rail gauges measured in the design process gave the required wheel to rail contact as demonstrated in the gauge lengths section of this paper. In figure 24 on the following page is the comparison between the theoretical point of the gauge length (left) and the actual contact point (right). Both coincide as an almost perfect match, which validates the equations carried out in the gauge lengths section, where the appropriate positions of the

23

holes connecting the middle square tubes to the wheel section were determined. The distance between the rail and the flange of the wheel allowed a smooth rolling motion without any interference, and as can be seen in the figure below on the right hand side, due to the rail grub (dirt) on the wheel, provided the proof of good rail to wheel contact, therefore fulfilling one of the aims of the project.

Figure 24. (Theoretical and real contact with the rail)

The rail buggy was not mounted with any analysis instrumentation on this occasion as this was a preliminary rail test to observe the response of the trolley in a real life situation. To scrutinize in depth the interaction between the wheel and the rail as motion took place, a video camera was employed, mounted to the structure by means of a band and a ruler as seen in Figure 25. As rudimentary as this set up may seem, it worked perfectly and gave a clear video of the interaction between the two components. This video showed the wheel rolling over the rail at a relatively constant speed and also showed the trolley going over a gap which separates the two rail sections, lasting approximately 60 seconds. This was carried out to observe the impact of rail separation on a miniature replica of a train wheel profile (P8 profile seen in appendix, page 31), as mentioned earlier on in the project.

Figure 25. (Video camera mounted on rail buggy)

Same point of contact

24

The design of the structure allowed the easy installation of the video camera on the rail buggy and also allowed this one to be perfectly centred with the rail as seen in figure 25. One of the aims of the project was to give a good configuration to allow the potential addition of instrumentation, this was meant to be a very easy exercise and as shown previously with the video camera, the addition of instruments does not require complex fastening methods. This was carefully thought through in the design process and was verified when the rail buggy was mounted on the rails. This can be seen in figure 26 below, demonstrating on the right hand side that the two 850mm square tubes used to connect the wheel units together were practically perfectly distributed on either side of the rail. The structure is very versatile, allowing endless additions and possibilities to the trolley which can be observed in Figure 26, in the full representation of the structure on the left hand side.

Figure 26. (Structure of the rail boggy)

An issue was noticed in the testing which had been overlooked during the design of the trolley, the existence of rail crossings and third rails, very present in modern railway systems. The rail crossing present at “Barrow Hill Train Yard”, did cause a problem to the rail buggy, as the bearing units came lower down than the portion of the wheel in contact with the rail, this can be observed in uigure 27. This issue was also noticed at the junction of rail systems due to the low height of the bearings. This effect meant that the rail boggy could not cross these obstacles by itself and therefore had to be lifted and carried beyond these points, an issue which could be very frustrating if attempting to monitor a rail segment situated in a rail crossing. The wheel would only require an additional 20mm in diameter to come well clear of these obstacles.

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Figure 27. (Rail boggy at a rail junction)

As can be seen in Figure 27, the bearing housings came in contact with the adjacent rail, preventing the wheels of the trolley to stay in contact with the carrying rail and also prevented motion by having a braking effect due to the rough contact of the two components. The third rail, commonly used in dc current powered trains did not have an effect on the trolley as the small size of the shaft and structure came reasonably clear from it, as can be observed below in figure 28.

Figure 28. (Rail buggy next to a sleeping third rail)

A colleague present during testing, sat on the rail buggy whilst it was being pushed along the rails. Her weight was concentrated on the aluminium plate situated on the back left wheel, this could be considered as an approximate 55kg mass which was applied on a singular wheel unit. The trolley did not show signs of strain at the area where the load was applied, neither did it generate any higher noise levels during operation. Going over a gap between two rail section, my colleague felt the defect very well through the insulating material, this said, the rail buggy did not feel much harder to push at any point during this particular test. After this exercise, it was found that her weight had made the insulating material compress so much that the wheel had rubbed on the aluminium plate, potentially explaining why the

Place of contact

Third rail

26

insulation had no damping effect and that she could feel the defects in the rails as going along. Due to the rubbing of the wheel against the aluminium plate in the loading exercise, a small dust of acetal was found on the component and it was clear that some material had been rubbed off the wheel in question; apart from this issue the wheel in question did not have any visible defects such as cracks or indentations of any kind and the structure of the trolley did not seem to have been affected in any way due to this imposed load. All the wheels were also examined after the day of testing for any type of defects, but none could be found apart from the vast amount of grub smeared in the wheels after being in contact with rusted rails and dirt, as can be seen on the left hand side of figure 28. The aluminium bolts, nuts and washers were also checked for grinding and defaults but apart from some paint having been removed, there were no visible defects on any of these components. As a whole, the structure seemed intact after this short day of testing, a longer period of time would be required to observe defects growing in the components of the rail buggy.

5.Design Review

The rail buggy successfully accomplish the aims of this project, such that it had good wheel to rail contact as demonstrated in the testing part of this paper, by conforming to the theoretical point of contact predicted in the design process. The wheels did not meet great interference at the intersection of rail sections. This said, no quantified load was added to the buggy in the testing, therefore all which is known is that unloaded, the rail buggy does not have any issues with travelling on rails. The exercise with the colleague sitting on the trolley presented some flaws in the implementation of insulating material between the two plates in the wheel unit, as when approximately 55kg was loaded on the aluminium plate, the wheel came into contact with the above plate causing some minor damage to the wheel, in the form of wear. A more selective loading exercise of the rail buggy would be necessary to quantify the compression of the insulating material per unit mass, which would then allow possible design changes to be made. These modifications such as a greater gap between the aluminium plate and the insulating material or a stiffer insulation, would potentially accommodate greater loads on the trolley, depending on the requirements set forward.The trolley design also allowed the possibility for it to be used on different rail gauge lengths, a matter which was not tested but could be deduced to be true as the holes on the 150mm aluminium square tube (see page 16), respected the difference in length between the gauge span selected in the relevant section of this paper. The calculations done for the United Kingdom gauge were right on the marks as determined in the testing, this allows the deductions that the other gauges selected would have a very similar contact with the rails. The access to rails with different rail gauges would have been of great interest to confirm this deduction, but this would require travelling which was unavailable in the time frame of this project.

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The cost of the unit was low considering that this was a prototype and that a production product would have a considerable lower cost to be manufactured as there would be a lower waste of materials and different manufacturing routes potentially taken. Looking at this from a different perspective, the majority of the manufacture was carried out by the university which generated no direct cost to the project. In a real life situation, labour would incur a cost which would be subjected to the total of the project. This said, the operations carried out by the university were basic, such as drilling, cutting and welding, which wouldn’t generate a high labour cost. The rail buggy does not have any means of motion such as a motor to drive or a handle to push, and the addition of such components would engender an increase in the overall cost due to the requirements of additional material and labour. The cost of the project increased to satisfy the low-weight requirements of the project, due to the use of 6000 series aluminium alloy over medium carbon steel. This change was necessary to allow a single person to carry the trolley conveniently, to and away from a testing ground. The final cost of this project is hard to compare to any existing products on the market as companies are very discreet about openly showing the cost of their products. In the present state the rail buggy is not marketable but due to its lightweight and effectiveness, with a few modifications and some additional trials it would be. The rail buggy could be considered light weight, as it respected the criteria of the project in such that a single person could carry it around with relative ease. The components which were the most influential toward the total mass of the trolley were the bearings with a cumulative mass of 7.16 kilograms, which is 30.4 per cent of the overall mass of the rail buggy. This is followed by the 25mm diameter bearing shaft with a cumulative mass of 3.86 kilograms, 16.4 per cent of the overall mass. These two components put together incur 46.8 per cent of the overall mass of the trolley and as shown in the stress analysis of the components, there was not a particular need for such heavy duty parts to be used in a trolley of 23.53 kilograms with the potential to carry a few additions. The load capacity of these members is shown in the structure part of this paper where an “Ansys Workbench” model was generated to demonstrate the load limit of the bearings and the shaft, which demonstrates, considering that all components are made out of average yield strength medium carbon steel, that 3.37 tonnes can be applied on each individual bearing housing before plastic deformation. This is not the representation of a safe load for the bearings but a mere representation of the extent of the strength of these components, such that the acetal wheel would fail much earlier, at 678kg evenly distributed per bearing housing. Adjusting this gap could result in a much lighter rail buggy which would still respect the aims of the project.The only main issue with the present design of the rail buggy is the fact that it interferes with rail crossings due to the low height of the bearing units. This discovery in the testing requires the change of a few components such as the wheel, insulation, plates and potentially even the steel bolts used in the wheel unit. Only an additional 20mm is required to the diameter of the wheels to come clear of this obstruction but on such a precise design, this requires the changes previously mentioned.

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6.Conclusion

The project was a successful enterprise as it satisfied all the aims listed at beginning of the paper. The rail buggy was a lightweight structure as its final mass was only 23.53kg, which allowed a single person to carry the product with relative ease, especially since the weight was distributed into two carrying bags instead of a single one. The project came at a relatively low cost considering that this was a prototype. The total cost of the project came to £922.95. The rail buggy allowed the possibility to be used on four different rail gauges which were selected to accommodate countries close by to the United Kingdom and widely used in the world. This was done by the extendibility of the sections with the use of square tubes which had different fitting holes for different rail gauges, the smallest one being the standard rail gauge (United Kingdom, North America,...). The trolley also gave a good rail to wheel contact as demonstrated in the testing section of the paper, as the theoretical area of contact matched the true final build one; this designed contact allowed a smooth rolling action of the rail buggy on the rail with no interference. The structure designed for the rail buggy gave a great surface for the addition of commodities such as inspection technologies, a laptop and a drive system, this was mainly due to the “H” style aluminium square tubes used which overpass the rails in such a manner, allowing a resting surface equidistant from the rails. All the instruments and tools required to assemble and disassemble the trolley nicely fitted in these two bags, shown below in figure 29.

Figure 29. (Ice hockey bags used in the project)

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7.References

1. Dobson, G. (2004). Civil protection, the fire and rescue service role, London Fire Brigade.

2. (2008). "Multi-Purpose Rail Trolley." from http://www.trackgeometry.co.uk/multi_purpose_trolley.htm.

3. (2008). "Railware Trolley." from www.plc2pc.com.4. Urs Müller, R. G., Gerard Peels, Alain Geiger (2004). "Precise Rail Track

Surveying." GPS World.5. Grassie, D. S. "Corrugation Analysis Trolley (CAT)." from

www.railmeasurement.com/cat.htm.6. group, mermec. (2009). "Rail Corrugation System - RCS." from

http://www.mermecgroup.com/pageview2.php?i=61&sl=1.7. Granta Design Limited. (2009). CES EduPack 2009. Cambridge.8. DemonXTREME Sports. (2009). "The Xtreme Ports Specialist." from

www.DemonXTREME.com.9. Knauf Insulation Ltd. "Rocksilk Universal Slab." from

www.knaufinsulation.co.uk.10. Lupton, J. Feasibility of reducing the number of standard

wheel profile designs. R. s. s. b. London.11. (2010). "Rail gauge." from http://en.wikipedia.org/wiki/Rail_gauge.12. Ross, C. T. F. (1987). Applied Stress Analysis, Ellis Horwood Limited13. "RS Components." from http://uk.rs-online.com/web/.

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Steel wheel

32

Acetal wheel

33